Metal focal plane shutters for cameras of the type in which an exposure is effected by the sequential operation of opening (leading) blades and closing (trailing) blades have been subject to the following faults.
Firstly, it is difficult to apply such shutters to miniature cameras because of the relatively large space required for containing the shutter blade groups. As a method of eliminating this fault, it has been proposed to make the space for containing the shutter blade groups smaller by dividing the shutters into a larger number of blades or by making the shutter blades smaller. However, in case of the former method, it has been found that the light tightness of the shutter deteriorates as the number of blades into which the shutter is divided increases. Also, the accuracy of the exposure and the endurance of the shutter are impaired because of the harmful effect arising from the increase of the inertial mass of the shutter blade groups. In the case of the latter method, the light tightness of the shutter is decreased because of the reduced overlap of the blades when in position to cover the aperture.
Secondly, a powerful driving force is required for actuating the shutter blade groups because of their large inertial mass. This results in a large force being required to set or cock the shutter and because of the forces involved, the durability of the shutter is impaired.
Thirdly, there is the fault of reexposure by reason of the rebound of the closing blades after finishing the exposing action when the blade speed is increased for obtaining a short exposure or for actuating the shutter by shorter speed thereof for flash synchronization.